Clasie made his debut for Saints in Saturday’s pre-season 3-0 victory over FC Groningen, a club dear to Koeman’s heart.
It was where the former Netherlands star made his professional debut as a teenager and his image still adorns photos on their walls.
His older brother Erwin Koeman, now assistant coach at Southampton, also played here, as did their father Martin. All were Dutch internationals and a stand at Groningen is named after their family in their honour.
Following Clasie’s debut in the Groningen match, Koeman told Sky Sports News HQ: “He’s a perfect replacement for Morgan in that position.
“i know that because I worked for three seasons with Jordi. Of course, he’s still not Schneiderlin – but he’s still young, he has to develop, he has to adapt to the Premier League, the intensity is what you need. It’s a great signing.”
He holds no hard feelings against Schneiderlin after the midfielder’s £25m switch to Manchester United.
“He’s a fantastic player,” Koeman said. “He did everything for the club and I think it was time for him, and I understand that.”
On Thursday, Koeman will take Southampton, and 24-year-old Clasie, back to another club which is close to his heart – Feyenoord.
Clasie, who was Koeman’s captain when he managed Feyenoord, said: “I played three years with Koeman. I’m happy that he trusts me and that he wants me to come to England.
“I’m proud that I can play in the Premier League.”
Clasie, who signed a five-year deal, made his debut in Ronald Koeman’s first game in charge at Feyenoord. He has since earned 11 international caps and was part of Louis van Gaal’s squad for the 2014 World Cup finals.